An image-acquisition device having an etalon spectroscopic element that can change the transmission band of light by changing the distance between surfaces of a plurality of substrates is known (for example, refer to Patent Document 1).
This image-acquisition device changes the transmission band of light emitted from an image-acquisition object with the etalon spectroscopic element to acquire spectroscopic information of the image-acquisition object. By changing the distance between the surfaces of the two substrates having coating layers, two different transmission characteristics are achieved. By calculating the difference between the intensity distributions of the images, spectrum analysis is performed.    Patent Document 1:    the Publication of Japanese Patent No. 2771785